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Disclosures: Haralampos M Moutsopoulos, MD, FACP, FRCP, Master ACR Nothing to disclose. George E Fragoulis, MD Nothing to disclose. John H Stone, MD, MPH Grant/Research/Clinical Trial Support: Roche [vasculitis (rituximab)]; Genentech [IgG4-related disease (rituximab)]. Consultant/Advisory Boards: Genentech [IgG4-related disease (rituximab)]; Bristol-Myers Squibb [(rituximab)]. Peter H Schur, MD Nothing to disclose. Paul L Romain, MD Employee of UpToDate, Inc.
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INTRODUCTION — Immunoglobulin G4-related disease (IgG4-RD) is an increasingly recognized syndrome of unknown etiology comprised of a collection of disorders that share specific pathologic, serologic, and clinical features . These different conditions were previously thought to be unrelated [2-4]. The commonly shared features include tumor-like swelling of involved organs, a lymphoplasmacytic infiltrate enriched in IgG4-positive plasma cells, and variable degrees of fibrosis that has a characteristic “storiform” pattern (picture 1). In addition, elevated serum concentrations of IgG4 are found in 60 to 70 percent of patients with IgG4-RD.
The majority of patients respond to glucocorticoids, particularly in early stages of disease. In some subsets of organ disease (eg, pancreatitis), glucocorticoid responsiveness has been considered one diagnostic criterion for the disorder.
Two major presentations of this condition, which often affects more than one organ, are type 1 autoimmune pancreatitis (IgG4-related pancreatitis) and salivary gland disease; the latter may present as salivary gland enlargement or as sclerosing sialadenitis (formerly termed “Mikulicz disease” and Küttner’s tumor, respectively). These conditions often resemble Sjögren’s syndrome but are pathophysiologically distinct from this disorder. The preferred name for the overall condition is IgG4-related disease [5,6]. However, multiple names have been employed to describe this entity [3,4]. These include:
This topic will provide an overview of the clinical manifestations, diagnosis, and treatment of IgG4-related disease and several of its component entities. Type 1 autoimmune pancreatitis (IgG4-related pancreatitis) and IgG4-related sclerosing cholangitis are discussed in detail separately (see "Autoimmune pancreatitis"), as are several of the other conditions associated with this disorder. (See appropriate topic reviews.)
DEFINITION AND HISTOLOGY — The hallmarks of IgG4-related disease (IgG4-RD) are lymphoplasmacytic tissue infiltration with a predominance of IgG4-positive plasma cells and T lymphocytes, usually accompanied by fibrosis, obliterative phlebitis, and elevated serum levels of IgG4 . A sizeable minority of patients (less than 40 percent) have normal serum IgG4 concentrations despite the presence of the classic histopathological changes in tissue . A good initial therapeutic response to glucocorticoids is characteristic, particularly if excessive tissue fibrosis has not supervened .
The fibrosis associated with IgG4-RD has a characteristic “storiform” pattern, typified by a cartwheel appearance of the arranged fibroblasts and inflammatory cells, termed the “nuclear streaming artifact” (picture 1) [7,10]. Modest tissue eosinophilia is also common.
EPIDEMIOLOGY — The overall disease epidemiology remains largely undefined. IgG4-RD is most often described as occurring in middle-aged and older men, but the sex distribution depends upon the index manifestation leading to study. Patients with type 1 autoimmune pancreatitis (IgG4-related pancreatitis), the best-studied group, are more often older men, although studies of IgG4-related sialadenitis have shown more equal sex distribution [3,11,12].
In a study of 114 patients with IgG4-RD, those with involvement limited to one of several regions (head and neck, thoracic, hepatopancreatobiliary, and retroperitoneal) and those with systemic involvement (more than one region) were compared with respect to various demographic and clinical features; the ages of patients in all groups were similar, with means from 59 to 68 years (ranges 42 to 79) . All the groups, other than the patients with head and neck involvement, were predominantly men (75 to 86 percent), but the group with only head and neck disease was nearly equally divided (48 percent men). Definitive assessments of the incidence and prevalence of IgG4-RD in the general population or among different geographic or ethnic populations are lacking.
PATHOGENESIS — The pathogenesis of IgG4-related disease (IgG4-RD) is poorly understood; findings consistent with both an autoimmune disorder and an allergic disorder are present [7,13-19]. IgG4 has been postulated to have a role in tolerance to allergens and in responses to certain infectious agents, but its physiologic role is poorly understood. A specific autoantigenic target has not been identified, and it is not clear whether the IgG4 antibodies are pathogenic . Elevations in serum and tissue IgG4 concentrations are not specific to IgG4-RD; they are also found in disorders such as multicentric Castleman’s disease, allergic disorders, the Churg-Strauss syndrome, sarcoidosis, and a large number of other conditions [21,22]. (See "IgG subclass deficiency", section on 'IgG4 deficiency' and "IgG subclasses: Physical properties, genetics, and biologic functions", section on 'Properties of IgG subclasses' and "Diagnostic evaluation of food allergy", section on 'Unvalidated methods' and "IgG subclasses: Physical properties, genetics, and biologic functions", section on 'Disorders associated with elevated subclass levels'.)
Findings in IgG4-RD suggesting autoimmunity have been particularly evident in patients with type 1 autoimmune pancreatitis (IgG4-related pancreatitis), the prototypic IgG4-related disorder, including an association with a specific class II histocompatibility antigen genotype . Antinuclear antibodies are sometimes present, and autoantibodies have been described against lactoferrin and carbonic anhydrase II. Some studies have suggested a possible role for molecular mimicry involving Helicobacter pylori . Immune complex deposition in the pancreas, kidneys, and certain other affected tissues has been reported . However, autoantibody studies have been inconsistent, and there is no definitive evidence for a role of autoimmunity in this disease. (See "Autoimmune pancreatitis".)
Evidence for an allergic response includes elevated levels of Th2 cytokines in affected tissues and increased amounts of serum IgE . In addition, patients with IgG4-RD have an increased prevalence of allergic rhinitis and bronchial asthma . There are increased numbers of T regulatory cells (Tregs) in peripheral blood and increased levels of cytokines produced by Tregs, including interleukin (IL)-10 and transforming growth factor (TGF)-β in affected tissues [16,17]. The Th2 cytokines, Tregs, and IL-10 help support IgG4 production [17,24]. Up to 40 percent of patients with IgG4-RD have a peripheral eosinophilia.
CLINICAL MANIFESTATIONS — IgG4-related disease (IgG4-RD) is a disorder that can involve one or multiple organs. Patients often present with subacute development of a mass in the affected organ (eg, an orbital pseudotumor, a renal mass resembling renal cell carcinoma, or nodular lesions in the lung) or diffuse enlargement of an organ (eg, the pancreas) [1,3,26]. Multiple organs are affected in 60 to 90 percent of patients with IgG4-RD [4,27]. The affected tissues share specific pathologic, serologic, and clinical features, regardless of the organ involved, in a manner analogous to the systemic involvement of sarcoidosis, another disorder with shared histopathologic features in the different tissues that are affected. Lymphadenopathy is common, and symptoms of asthma or allergy are present in approximately 40 percent of patients. Patients often feel well at the time of diagnosis and lack fever or other constitutional symptoms . IgG4-RD is also often recognized incidentally based upon a radiologic finding or histopathologic examination of a tissue specimen.
The disorder has been viewed as uncommon, but components of this syndrome are now increasingly recognized in nearly every organ system. Many of the initial observations regarding this condition were made in patients with autoimmune pancreatitis, which often presents as a pancreatic mass or as painless obstructive jaundice, and can be mistaken for pancreatic cancer. Additional reports have focused on patients with lacrimal and salivary gland involvement, formerly termed Mikulicz’s disease, which was once thought to be a subset of Sjögren’s syndrome (picture 2) [3,26]. Such patients may present, for example, with prominent parotid or submandibular gland enlargement. The terms IgG4-related dacryoadenitis and IgG4-related sialadenitis are now used in place of Mikulicz’s disease. IgG4-related dacryoadenitis and sialadenitis do not invariably occur together.
IgG4-RD associated disorders — Previously described conditions that represent manifestations of IgG4-RD and the nomenclature, when not otherwise indicated, include [3-5]:
Estimates of the relative frequency of different manifestations depend upon the particular perspective of the index illness being studied. As an example, a study of patients with autoimmune pancreatitis found frequent extrapancreatic involvement, including hilar lymphadenopathy (80 percent), extrapancreatic bile duct lesions (74 percent), lacrimal and salivary gland lesions (39 percent), hypothyroidism (22 percent), and retroperitoneal fibrosis (13 percent) . In contrast, autoimmune pancreatitis was found in only 17 percent of patients studied with IgG4-related lacrimal, parotid, or submandibular gland disease, and interstitial nephritis (17 percent) and interstitial pneumonitis (9 percent) were also seen among this group .
Lymphadenopathy — Asymptomatic IgG4-related lymphadenopathy is common, occurring in 80 percent of patients with autoimmune pancreatitis ; it is usually observed together with other clinical or laboratory manifestations of the syndrome but may be the initial or only manifestation . In a study of 114 patients with varied organ involvement, lymphadenopathy was present in 41 percent of patients . Symptoms occasionally occur due to mass effect of the enlarging nodes; individual nodes are typically no more than 2 centimeters in diameter but may range up to 5 centimeters . Multiple groups of lymph nodes are usually involved; the mediastinal, hilar, intra-abdominal, and axillary are most common and can be readily seen upon scanning with gallium-67 .
Five histologic patterns may be seen, which all feature abundant IgG4 positive cells; the majority have eosinophil infiltration [7,31-33]. Histology is similar to other affected tissues, except that there is usually no sclerosis or phlebitis. The patterns include:
Patients with lymphadenopathy may exhibit elevated serum IgG4, serum IgG and IgE, polyclonal hypergammaglobulinemia, and elevations in the erythrocyte sedimentation rate.
The differential diagnosis in patients with generalized lymphadenopathy includes lymphoma, multicentric Castleman disease, or malignancy. IgG4-related lymphadenopathy is distinguished from these conditions by the modest lymph node enlargement, histologic distinctions on biopsy, lack of constitutional features, and the usually striking clinical response to glucocorticoids . Patients with bilateral hilar adenopathy may mimic sarcoidosis. (See "Evaluation of peripheral lymphadenopathy in adults" and "Clinical presentation and diagnosis of non-Hodgkin lymphoma" and "Epidemiology, pathologic features, and diagnosis of classical Hodgkin lymphoma" and "Multicentric Castleman's disease" and 'Lung and pleural disease' below.)
Autoimmune pancreatitis — Type 1 autoimmune pancreatitis (IgG4-related pancreatitis) is the prototypical form of IgG4-RD. The prevalence of this condition in Japan has been estimated to be 0.82 per 100,000 persons, but this is likely to be an underestimate as clinical recognition of this disorder is growing [34,35]. Two types of autoimmune pancreatitis (AIP) have been distinguished; the form associated with IgG4-RD is type 1 AIP, also denoted as lymphoplasmacytic sclerosing pancreatitis . AIP is discussed in detail separately. (See "Autoimmune pancreatitis".)
AIP has been estimated to account for 2 percent of patients with chronic pancreatitis . It often presents as a pancreatic mass or as painless obstructive jaundice and can be mistaken for pancreatic cancer. Some patients with type 1 AIP exhibit acute, recurrent, or chronic pancreatitis, and AIP is frequently associated with diabetes mellitus. Most patients have another IgG4-related condition, such as IgG4-related sclerosing cholangitis, lymphadenopathy, or salivary or lacrimal gland involvement. (See 'Clinical manifestations' above and "Autoimmune pancreatitis".)
The differentiation of AIP from adenocarcinoma of the pancreas is sometimes difficult on the basis of clinical presentations. Painless jaundice, for example, is common to both. Many patients have undergone Whipple procedures with the intention of treating pancreatic cancer. IgG4-positive plasma cells can also be found in the diseased pancreatic tissue in these conditions, although to a lesser degree than in AIP. Elevated serum IgG4 levels (>135 mg/dL) can also be seen in some patients with pancreatic cancer, although they are usually less than twice the upper limit of normal; thus, increased IgG4 serum levels alone cannot be used to exclude a diagnosis of pancreatic malignancy . Radiologic features of type I AIP include diffuse enlargement of the pancreas, leading to the descriptor “sausage-shaped” pancreas, and a halo of edema surrounding the organ. Both of these features are appreciated most readily on abdominal computerized tomographic (CT) scanning.
IgG4-related sclerosing cholangitis — A form of sclerosing cholangitis that is clinically distinct from primary sclerosing cholangitis may occur as part of the IgG4-RD. IgG4-related cholangitis is the most frequent extrapancreatic manifestation of type 1 AIP (IgG4-related), present in over 70 percent of such patients . It also rarely occurs in the absence of pancreatitis. The clinical distinction between primary sclerosing cholangitis and IgG4-related sclerosing cholangitis can be difficult [17,37], but attempts to do so are critical because of the drastically different prognoses in these conditions. (See "Autoimmune pancreatitis", section on 'Biliary tract manifestations' and "Primary sclerosing cholangitis in adults: Clinical manifestations and diagnosis", section on 'Differential diagnosis'.)
Salivary and lacrimal gland involvement — Salivary gland involvement is a common feature of IgG4-RD. Patients may present with enlargement of lacrimal and salivary glands (parotid and/or submandibular) or with chronic sclerosing sialadenitis and unilateral or bilateral submandibular gland enlargement . These entities were previously called Mikulicz disease (or syndrome) and Küttner tumor, respectively, and were often erroneously considered to be subcategories of Sjögren's syndrome (SS) (picture 2) [11,20,38-43]. Many of the patients previously described as having SS in association with AIP and IgG4-RD may have had one of these conditions rather than true SS. (See "Classification and diagnosis of Sjögren's syndrome", section on 'Mikulicz syndrome and IgG4-related disease' and "Salivary gland tumors: Epidemiology, diagnosis, evaluation, and staging".)
Nearly 40 percent of patients with IgG4-related pancreatitis also have salivary or lacrimal gland involvement, while AIP may be seen in only 17 percent of patients presenting with sialadenitis [11,28]. Sialadenitis often presents prior to AIP in patients who develop both conditions . Unlike AIP and other forms of IgG4-RD, patients with salivary and lacrimal involvement include comparable numbers of both men and women [11,12]. The pathologic findings are typical of those in other patients with IgG4-RD, including the lymphoplasmacytic infiltrate with IgG4-positive cells, sometimes with obliterative phlebitis and fibrosis (picture 3 and picture 4) . Increased IgG4 and IgE serum levels are also present. These histopathologic and laboratory findings distinguish IgG4-related sialadenitis from SS. Low complement levels may be seen in either condition.
The clinical features that characterize IgG4-related sialadenitis and also distinguish it from SS include :
Two of the authors (HM and GF) have observed that there are some patients who fulfill classification criteria for both SS and IgG4-RD. Further studies are needed to explore the possible coexistence of both entities in the same patients.
Patients with IgG4-related ophthalmic disease, primarily involving the lacrimal gland (IgG4-related dacryoadenitis), have also been identified [45,46]. Many exhibited bilateral involvement, and concurrent salivary gland involvement was common. Histologic and serologic findings are similar to those seen in patients with sialadenitis and in other tissues, although obliterative phlebitis is usually absent. IgG4-RD also appears to account for 25 to 50 percent of orbital pseudotumors and is additionally recognized now as a cause of orbital myositis (IgG4-related orbital myositis) [47,48].
It is not certain whether IgG4-RD predisposes to the development of ocular adnexal mucosa-associated lymphoid tissue (MALT) lymphomas or other lymphomas, but several cases have been reported that have raised this concern [49-51]. Additional study is required.
Retroperitoneal fibrosis and related disorders — In several small case series, a variable proportion of patients with idiopathic retroperitoneal fibrosis exhibits histologic and serologic changes consistent with IgG4-RD [52-56]. Chronic inflammatory and fibrotic change may be present and can involve regional tissues; it may cause an obstructive uropathy. In some cases, the syndrome is responsive to glucocorticoids. The diagnosis of IgG4-RD in this setting can be challenging because of the advanced fibrotic changes typically observed in this condition. Retroperitoneal fibrosis is discussed in detail elsewhere. (See "Clinical manifestations and diagnosis of retroperitoneal fibrosis" and "Treatment of retroperitoneal fibrosis".)
All 14 of the published cases of IgG4-related retroperitoneal fibrosis collected in one review exhibited involvement of other organs, including the pancreas (11 patients), salivary glands (3 patients), lymph nodes (2 patients), one affecting the pituitary gland, and one with mediastinal periaortitis . However, cases of isolated IgG4-related retroperitoneal fibrosis have also been described .
Cases of patients with sclerosing mesenteritis, sclerosing mediastinitis, and multifocal fibrosclerosis have also been reported associated with IgG4-RD [58-60]. (See "Sclerosing mesenteritis", section on 'Autoimmunity' and "Fibrosing mediastinitis", section on 'Other precipitants'.)
Aortitis and periaortitis — IgG4-RD has been recognized as one of the causes of noninfectious aortitis . A series of patients with thoracic lymphoplasmacytic aortitis or with inflammatory abdominal aortic aneurysms and abdominal periaortitis has been identified in retrospective pathologic studies of patients who had undergone aortic resections [55,61,62]. (See "Epidemiology, risk factors, pathogenesis and natural history of abdominal aortic aneurysm", section on 'Pathogenesis' and "Clinical manifestations and diagnosis of thoracic aortic aneurysm".)
Thyroid disease — Two forms of thyroid involvement in IgG4-RD have been described, including Reidel’s thyroiditis (IgG4-related thyroid disease) and the fibrous variant of Hashimoto’s thyroiditis [64,65]. Reidel’s thyroiditis is discussed in detail elsewhere. (See "Infiltrative thyroid disease", section on 'Riedel's thyroiditis'.)
Lung and pleural disease — Multiple reports have documented IgG4-related pulmonary disease, which may be asymptomatic or present with cough, hemoptysis, dyspnea, pleurisy, or chest pain; pseudotumors and interstitial pneumonia have been associated with AIP [66-70]. Visceral or parietal pleural thickening may occur. The affected tissues exhibit characteristic lymphoplasmacytic infiltrates enriched in IgG4-positive plasma cells. Obliterative arteritis is more common in the lung than in other organs affected by IgG4-RD . Four patterns of lung involvement have been described [70,71]:
IgG4-RD may mimic sarcoidosis [72,73]. In one study of patients suspected of having sarcoid with bilateral hilar adenopathy and/or lung nodules on computerized tomography (CT) of the chest, patients with IgG4-RD were identified among a subset with elevated serum IgG4; they exhibited significantly higher levels of bronchoalveolar lavage IgG4, IgG4/IgG, and IgG4/IgG3 compared with those with normal serum IgG4 levels .
Interstitial pneumonitis associated with IgG4-RD is discussed separately. (See "Interstitial lung disease associated with Sjögren's syndrome: Clinical manifestations, evaluation, and diagnosis", section on 'IgG4-related systemic disease'.)
Renal disease — Individual cases and case series have described renal involvement in patients with IgG4-RD; the most common finding is tubulointerstitial nephritis [74-77]. Affected patients are primarily middle-aged and older men, and histopathology and other laboratory characteristics are similar to those observed in patients with autoimmune pancreatitis (AIP) . The histologic findings include lymphoplasmacytic infiltration of the renal interstitium with increased numbers of IgG4-positive plasma cells and the presence of fibrosis. Nodular lesions mimicking renal carcinoma may be seen.
In a study of 153 patients with suspected IgG4-related disease, retrospectively collected from multiple medical centers in Japan, 23 patients (15 percent) were identified with tubulointerstitial nephritis (TIN) secondary to IgG4-RD, all but one of whom (96 percent of TIN patients) exhibited involvement of other organs . These extrarenal manifestations included sialadenitis (83 percent), lymphadenopathy (44 percent), AIP (39 percent), dacryoadenitis (30 percent), lung lesions (26 percent), and others in individual patients. In addition to TIN, 3 of the 23 patients also had mild mesangioproliferative glomerulonephritis (GN), and one each had findings of membranous nephropathy and of focal segmental endocapillary hypercellularity.
Symptoms were usually associated with the extrarenal manifestations, rather than the renal abnormalities, although edema was seen in two patients. Renal changes were recognized due to urinary abnormalities, renal dysfunction, and/or imaging abnormalities, including renal parenchymal lesions on computerized tomography and increased renal uptake with gallium citrate scintigraphy.
IgG4-related membranous nephropathy is much less frequent than IgG4-related TIN, and these sometimes occur together . In a series of nine patients with IgG4-related membranous GN, five of the patients had concurrent IgG4-related TIN, and seven exhibited extrarenal involvement by IgG4-RD [78,79]. None of the patients with IgG4-related disease were positive for phospholipase A2 receptor on biopsy, although it is present in a majority of patients with primary membranous GN. (See "Causes and diagnosis of membranous nephropathy", section on 'IgG4-related disease'.)
Other involved organs and tissues — Involvement of other organs and tissues by IgG4-RD, which has been described in additional case reports and small case series, includes:
DIAGNOSIS — The diagnosis of IgG4-RD is based upon biopsy findings demonstrating the characteristic histopathologic findings and immunohistochemical staining. These findings include lymphoplasmacytic tissue infiltration of mainly IgG4-positive plasma cells and small lymphocytes, accompanied by fibrosis that has storiform features and often by obliterative phlebitis. A modest tissue eosinophilia is often present. Serum IgG4 levels should be measured, and isolated elevated levels are a significant aid in diagnosis, although they are not diagnostic. The histopathological and immunohistochemical staining features of IgG4-RD are strikingly similar in different tissues, regardless of the organ or tissue involved. (See 'Diagnostic criteria' below.)
Indications for diagnostic evaluation — The possibility of IgG4-RD should be considered in patients with one of the characteristic patterns of organ or tissue involvement. (See 'IgG4-RD associated disorders' above.)
Patients at high risk for having IgG4-RD are those with any of the following:
The likelihood of IgG4-RD for patients presenting with at least one of these conditions is significantly increased if high serum levels of IgG4, allergic symptoms, and/or other fibrotic processes, such as retroperitoneal fibrosis, are also present.
Diagnostic studies — The diagnosis of IgG4-RD requires characteristic findings upon biopsy of affected tissue, but additional organ involvement may be possible to identify through a careful history, physical examination, routine laboratory testing, and selected imaging studies. (See 'Clinical manifestations' above and 'Diagnosis' above.)
We obtain the following testing for establishing the initial diagnosis:
Diagnostic criteria — A consensus statement from a multinational, multidisciplinary group of experts on IgG4-RD describes guidelines for the diagnosis of the disease and the histopathologic findings important in making the diagnosis . Well-defined diagnostic criteria had previously been proposed only for autoimmune pancreatitis (AIP). The histopathological findings of a dense lymphoplasmacytic infiltrate, storiform fibrosis, and obliterative phlebitis are critical features for establishing the diagnosis in affected tissues other than lymph nodes (picture 1). The presence of these findings, often together with mild tissue eosinophilia, is strongly suggestive if accompanied by increased numbers of IgG4-positive plasma cells. (See "Autoimmune pancreatitis", section on 'Diagnosis'.)
The number of IgG4-positive plasma cells per high power field (HPF) regarded as sufficient varies somewhat from tissue to tissue, and tissue IgG4-positive cell counts and the ratios of IgG4- to IgG-positive cells are considered secondary in importance [3,7,12,40,95]. Generally, the minimum for making the diagnosis for most tissues is from 30 to 50 IgG4-positive cells/HPF. However, in some organs or tissues, including the kidney and others, only 10 IgG4-positive plasma cells/HPF may be sufficient.
The diagnosis cannot be predicated entirely upon the number of IgG4-positive plasma cells, because a large number of other entities can have such cells, nor can the diagnosis of IgG4-RD be based upon serum concentrations of IgG4 alone. Serum IgG4 concentrations are neither sufficiently sensitive nor specific for this disease. Thus, we strongly prefer confirmation of the diagnosis by biopsy of an involved organ whenever this is possible.
Postdiagnostic evaluation — We obtain the following testing for establishing the extent of disease following the initial diagnosis:
DIFFERENTIAL DIAGNOSIS — The differential diagnosis of IgG4-related disease is broad and depends upon the specific site of involvement and clinical presentation (see appropriate heading above and see appropriate topic reviews).
TREATMENT — The optimal treatment for IgG4-related disease (IgG4-RD) has not been established. Our approach to treatment of IgG4-RD is based upon observational data, including case reports and case series, almost all of which have focused on patients with autoimmune pancreatitis (AIP), and upon our clinical experience with patients with other forms of IgG4-RD . There are no randomized trials that have evaluated approaches to the treatment of IgG4-RD or type 1 AIP. (See "Autoimmune pancreatitis", section on 'Treatment' and "Autoimmune pancreatitis", section on 'Glucocorticoids'.)
Most patients respond to glucocorticoids within several weeks, typically with symptomatic improvement, reductions in the size of masses or organ enlargement, improvement in organ function, and often a decrease in serum levels of IgG4. However, some require a few months to respond, and there are some patients who relapse and others who respond less well or not at all initially. Those who respond less well may include patients with more advanced fibrotic changes, but these patients have not been well-defined. A responder index is under development for use in clinical research to assess patient outcomes . The treatment of AIP and the evidence supporting the use of these therapies is discussed in detail elsewhere.
Patients who are symptomatic from their organ involvement at the time of the diagnosis often benefit from treatment. Examples of such symptomatic involvement include patients with lacrimal gland swelling or other orbital pseudotumors, who may have significant proptosis; those with submandibular or parotid gland swelling, who may have pain from their glandular enlargement or concern about cosmetic issues; those with renal involvement, who may have kidney dysfunction due to tubulointerstitial nephritis; and those with type I autoimmune pancreatitis (AIP) or retroperitoneal fibrosis, who may have abdominal or flank pain or other manifestations of their organ involvement. All of these patients need to be treated. In contrast, for a subset of patients such as those who have mild lymphadenopathy or incidentally-detected lung nodules, watchful waiting may be appropriate.
We suggest beginning treatment with orally administered prednisone, usually at a dose of approximately 40 mg/day. A response is frequently seen within two to four weeks. Once a significant response is clinically evident in the affected organ system, we begin to gradually taper the dose of glucocorticoids, with a planned reduction over a two-month period, as tolerated, with the goal of discontinuing the medication.
In patients who are resistant to glucocorticoids or who are unable to have their dose reduced sufficiently (usually to below 10 mg/day of prednisone) to avoid adverse effects of the medication due to chronic use, we use azathioprine (2 mg/kg/day) or mycophenolate mofetil (up to 2.5 g/day as tolerated). However, the effects of these glucocorticoid-sparing medications in IgG4-RD have not been evaluated adequately to clearly define their role relative to other agents. (See "Autoimmune pancreatitis", section on 'Treatment' and "Autoimmune pancreatitis", section on 'Immunomodulatory drugs'.)
PROGNOSIS — The natural history of IgG4-RD has not been well-defined; some patients improve spontaneously without treatment, but many relapse in time [7,97]. Causes of significant morbidity and mortality in untreated patients include cirrhosis and portal hypertension; retroperitoneal fibrosis; complications from aortic aneurysms, including dissection; biliary obstruction; diabetes mellitus; and others [53,61,97,101,102]. Sustained benefit may be observed in treated patients, but relapses are common after discontinuation of therapy. Additional organs and tissues may become involved over time, sometimes despite apparently effective treatment. Additional studies of long term prognosis are needed.
Risk of malignancy — Several types of lymphoma have been reported in patients with IgG4-RD, both in Japan and in North America [7,45,49,103,104]. In the study in North America, which involved 111 patients with IgG4-RD (91 percent with AIP), three cases of non-Hodgkin lymphoma were found three to five years after the diagnosis of IgG-RD . The standardized incidence ratio was 16.0 (95% CI 3.3-45.5), suggesting an increased risk of non-Hodgkin lymphoma among this group of patients referred to an academic medical center with special interest in this disorder. Further studies are required to better define the degree of risk and the effect of treatment upon such risk, if present.
In one series of 108 Japanese patients with IgG4-related pancreatitis, 18 cancers were found in 15 patients (14 percent); the median follow-up was 3.3 years . At the time of diagnosis of the pancreatitis, the relative risk (RR) of cancer was significantly increased compared with age- and sex-matched controls (RR 4.9, 95% CI 1.7-14.9); the risk was highest in the year following diagnosis. Gastric cancers were the most common; other sites included lung, prostate, colon, non-Hodgkin lymphoma, bile duct, and thyroid. In six of eight patients whose cancer was assessed histologically before treatment with glucocorticoids for the pancreatitis, IgG4-positive plasma cell infiltrates were found in the cancer tissue. None of these patients experienced relapse of their IgG4-related pancreatitis after successful treatment of their cancers, raising the question of whether IgG4-RD may occur as a paraneoplastic syndrome in some patients.
Several cases of pancreatic cancer and cases of salivary duct carcinoma, pulmonary adenocarcinoma, small cell carcinoma of the lung, and gastrointestinal clear cell sarcoma have also been reported . Additional study is required to determine the degree, if any, of increased risk for these and other malignancies in affected patients.
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